1. Field of the Invention
This invention relates to a treatment device utilizing plasma, which is suitable for etching treatment or cleaning removal treatment of silicon or silicon compound in a plasma atmosphere of fluorin or fluorin compound, or for thin film formation treatment to deposit a thin film of silicon on silicon compound on a support.
2. Description of the Prior Art
In the prior art, structural members for vacuum device have been desired to have surfaces which are stable chemically and thermally, and to emit gases in an amount as small as possible when under vacuum.
For this reason, as a general practice, stainless steels have been used for structural members in vacuum devices for which vacuum of high quality is required in connection with semiconductors.
The situation is the same in gas-phase method devices, and stainless steels have been used not only for vacuum tanks but also for internal implements such as high frequency electrodes.
However, in plasma etching devices employing these stainless steels, when forming, for example, semiconductor circuits by etching of silicon wafer with the use of a fluorocarbon type gas such as CF.sub.4 as the etching gas, the surface of the stainless structural member exposed to the plasma atmosphere will be corroded with fluorine radicals formed in said plasma, whereby milky white iron trifluoride (FeF.sub.3) powder will be formed on the surface.
This FeF.sub.3 is formed on the surface of stainless steel through the chemical reaction between fluorine radicals and iron contained as the main component of stainless steel. Consequently, deterioration in strength of the stainless structural member and contamination within the reaction chamber by fluorine will proceed.
Further, FeF.sub.3 formed and deposited on the surface of stainless structural member is very fragile and thus can be readily peeled off from the structural member surface, with the fragments of FeF.sub.3 floating in the reaction chamber until attached on the surface of the material to be etched, which may cause generation of undesirable failures in etching.
Among the examples of the prior art, it is also proposed to use SUS 316 steel with lower iron content as compared with SUS 304 steel as the anticorrosive structural member. Even in such a structural member, since the main component is iron, a minute amount of FeF.sub.3 will be formed on its surface, thereby causing formation of dust and fluorine contamination. Also, in the case when forming a vapor deposited film on a substrate in a plasma atmosphere of SiF.sub.4, there will ensue a similar problem on account of FeF.sub.3 formed from the stainless structural member within the gas-phase method device. Further, when a deposited layer is formed in the gas-phase method device according to such a method as heating vapor deposition, sputtering vapor deposition, electron beam vapor deposition or CVD (chemical vapor deposition), the material to be deposited will be adhered even onto the portions other than the substrate for deposit formation within the gas-phase method device. If such adherents are left to remain as such, inconveniences will be brought about similarly as in the case of iron trifluoride. Therefore, also in the case of removing these adherents by cleaning with a plasma atmosphere of a fluorine compound gas, the stainless structural member in the gas-phase method device reacts with the gas to form iron trifluoride, thus posing the problem that the object of cleaning cannot be accomplished.